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Questions and Answers
Which process best illustrates catabolism?
Which process best illustrates catabolism?
What characterizes autotrophs?
What characterizes autotrophs?
Which term represents the change in free energy during a chemical reaction?
Which term represents the change in free energy during a chemical reaction?
According to the first law of thermodynamics, what is true?
According to the first law of thermodynamics, what is true?
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Which of the following best describes the concept of entropy?
Which of the following best describes the concept of entropy?
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What is the significance of the standard free-energy change, ∆G′°?
What is the significance of the standard free-energy change, ∆G′°?
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Which statement explains the relationship between anabolism and catabolism?
Which statement explains the relationship between anabolism and catabolism?
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Which biochemical reaction is characterized by the transfer of a phosphate group?
Which biochemical reaction is characterized by the transfer of a phosphate group?
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Which type of system is characterized by the exchange of material and energy with its surroundings?
Which type of system is characterized by the exchange of material and energy with its surroundings?
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What does a negative ∆H value indicate about a reaction?
What does a negative ∆H value indicate about a reaction?
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What is the role of the standard equilibrium constant, K′eq, in reactions?
What is the role of the standard equilibrium constant, K′eq, in reactions?
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Which thermodynamic process is described by an increase in entropy?
Which thermodynamic process is described by an increase in entropy?
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In a system where ∆G is positive, which statement is true?
In a system where ∆G is positive, which statement is true?
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What does the equation ∆G = ∆H − T∆S tell us about spontaneity?
What does the equation ∆G = ∆H − T∆S tell us about spontaneity?
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Which of the following best represents the change in energy capable of doing work during a reaction?
Which of the following best represents the change in energy capable of doing work during a reaction?
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When discussing the effect of breaking glycosidic linkages, which thermodynamic quantity is most directly relevant?
When discussing the effect of breaking glycosidic linkages, which thermodynamic quantity is most directly relevant?
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Which statement about entropy is NOT accurate?
Which statement about entropy is NOT accurate?
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In a reaction where ∆S is negative, what can be concluded about the complexity of the reactants and products?
In a reaction where ∆S is negative, what can be concluded about the complexity of the reactants and products?
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What characterizes an endergonic reaction?
What characterizes an endergonic reaction?
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What is the value of the Boltzmann constant?
What is the value of the Boltzmann constant?
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At which temperature does RT equal 2.478 kJ/mol?
At which temperature does RT equal 2.478 kJ/mol?
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What is the unit of measurement for the change in entropy, ΔS?
What is the unit of measurement for the change in entropy, ΔS?
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A reaction with ∆H < 0 and ∆S > 0 is characterized as which of the following?
A reaction with ∆H < 0 and ∆S > 0 is characterized as which of the following?
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What is the standard free-energy change related to when discussing equilibrium constants?
What is the standard free-energy change related to when discussing equilibrium constants?
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What is Avogadro's number used to represent?
What is Avogadro's number used to represent?
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How does a system that follows the second law of thermodynamics behave?
How does a system that follows the second law of thermodynamics behave?
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What is the equation representing the relationship between ΔG0 and Keq at equilibrium?
What is the equation representing the relationship between ΔG0 and Keq at equilibrium?
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What dimensionless numbers correspond to the conditions K > 1, K < 1, and K = 0 in terms of equilibrium state?
What dimensionless numbers correspond to the conditions K > 1, K < 1, and K = 0 in terms of equilibrium state?
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Which physical constant is equivalent to 8.315 J/mol K?
Which physical constant is equivalent to 8.315 J/mol K?
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What is the standard free-energy change related to the equilibrium constant of a reaction where Keq = 0.1?
What is the standard free-energy change related to the equilibrium constant of a reaction where Keq = 0.1?
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What would be the expected sign for ∆G′° if K′eq is much greater than 1?
What would be the expected sign for ∆G′° if K′eq is much greater than 1?
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To calculate the transformed free energy required to provide cells with a certain concentration of ATP, which values must be used in the equation ∆G′° = -RT ln K′eq?
To calculate the transformed free energy required to provide cells with a certain concentration of ATP, which values must be used in the equation ∆G′° = -RT ln K′eq?
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Using the given values of R and T, what is the purpose of calculating ∆G′° in biochemical reactions?
Using the given values of R and T, what is the purpose of calculating ∆G′° in biochemical reactions?
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In a scenario where K′eq = 4 x 10^9, what can be inferred about the value of ∆G′°?
In a scenario where K′eq = 4 x 10^9, what can be inferred about the value of ∆G′°?
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How does the standard biochemical state for [H+] typically defined?
How does the standard biochemical state for [H+] typically defined?
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If a reaction at standard conditions has a ∆G′° of -11.5 kJ/mol, what does this imply about K′eq?
If a reaction at standard conditions has a ∆G′° of -11.5 kJ/mol, what does this imply about K′eq?
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Which constant is used in the equation to relate K′eq and ∆G′°?
Which constant is used in the equation to relate K′eq and ∆G′°?
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What is the standard transformed concentration of [H2O] under biochemical standard conditions?
What is the standard transformed concentration of [H2O] under biochemical standard conditions?
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What does a K′eq value greater than 1 indicate about the direction of the reaction?
What does a K′eq value greater than 1 indicate about the direction of the reaction?
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In a reaction where K′eq is equal to 1, what can be inferred about the Gibbs free energy change (ΔG′°)?
In a reaction where K′eq is equal to 1, what can be inferred about the Gibbs free energy change (ΔG′°)?
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What is the consequence of a negative ΔG′° value in terms of the reaction's behavior?
What is the consequence of a negative ΔG′° value in terms of the reaction's behavior?
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Which of the following statements about the equilibrium constant K′eq is incorrect?
Which of the following statements about the equilibrium constant K′eq is incorrect?
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If a biochemical reaction has ΔG′° equal to zero, what does this imply about the concentrations of reactants and products?
If a biochemical reaction has ΔG′° equal to zero, what does this imply about the concentrations of reactants and products?
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Which statement about a carbanion is true?
Which statement about a carbanion is true?
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What role does a carbonyl group play in aldol condensation reactions?
What role does a carbonyl group play in aldol condensation reactions?
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Which statement about carbocations is incorrect?
Which statement about carbocations is incorrect?
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Which process is primarily associated with the formation of a carbon–carbon bond?
Which process is primarily associated with the formation of a carbon–carbon bond?
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What is one characteristic of homolytic cleavage?
What is one characteristic of homolytic cleavage?
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What typically enhances the delocalization of electrons in carbonyl and imine groups?
What typically enhances the delocalization of electrons in carbonyl and imine groups?
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Which statement about the oxidation states of carbon is true?
Which statement about the oxidation states of carbon is true?
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What occurs during redistribution of electrons in internal rearrangements?
What occurs during redistribution of electrons in internal rearrangements?
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What type of reaction involves the transfer of acyl groups?
What type of reaction involves the transfer of acyl groups?
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Study Notes
Bioenergetics and Thermodynamics
- Bioenergetics is the study of energy transformations in living organisms.
- Energy transductions are changes of one form of energy into another.
- Living organisms follow the laws of thermodynamics.
- The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed.
- The Second Law of Thermodynamics states that the universe always tends toward increasing disorder.
- System is the collection of matter undergoing a chemical or physical process; it can be closed or open.
- Surroundings are everything outside of the system.
- Universe encompasses the system and its surroundings.
- Living cells and organisms are open systems, exchanging material and energy with their surroundings.
Enthalpy
- Enthalpy (H) represents the heat content of a system.
- The enthalpy change (∆H) is the difference in heat content between products and reactants.
- Negative ∆H indicates an exothermic reaction, where heat is released.
- Positive ∆H indicates an endothermic reaction, where heat is absorbed.
Entropy
- Entropy (S) quantifies the randomness or disorder of a system.
- Entropy change (∆S) represents the difference in disorder between products and reactants.
- Negative ∆S indicates lower disorder in the products compared to reactants.
- Positive ∆S indicates higher disorder in the products compared to reactants.
Free Energy
- Free energy (G) represents the amount of energy available to do work under constant temperature and pressure.
- Free-energy change (∆G) is the difference in free energy between products and reactants.
- Negative ∆G indicates an exergonic reaction, where free energy is released, and the reaction is spontaneous.
- Positive ∆G indicates an endergonic reaction, where free energy is absorbed, and the reaction is non-spontaneous.
Free-Energy Change Equation
- ∆G = ∆H − T∆S (Equation 13-1)
- Negative ∆H contributes to a negative ∆G: heat is released.
- Positive ∆S contributes to a negative ∆G: disorder increases.
Discussion/Question
- Breaking the α(1→4) O-glycosidic linkages in maltose would release energy, indicating a negative enthalpy change (∆H).
- If the reaction is assumed to have no heat exchange (∆H=0), the system's randomness (entropy change, ∆S) plays a major role.
- Therefore, the thermodynamic quantity MOST related to breaking the linkage is entropy (B).
Physical Constants and Units Used in Thermodynamics
- Boltzmann constant: k = 1.381 × 10−23 J/K
- Avogadro's number: N = 6.022 × 1023 mol−1
- Faraday constant: F = 96,480 J/V mol
- Gas constant: R = 8.315 J/mol K
- R = 1.987 cal/mol K
- Units of ΔG and ΔH are J/mol (or cal/mol)
- Units of ΔS are J/mol K (or cal/mol K)
- 1 cal = 4.184 J
- Units of absolute temperature, T, are Kelvin, K
- 25 °C = 298 K
- At 25 °C, RT = 2.478 kJ/mol
- RT = 0.592 kcal/mol
Living Cells and the Second Law of Thermodynamics
- Living organisms create order within their cells as they grow and divide.
- This order is compensated for by the disorder they create in their surroundings.
- Living organisms take free energy from their surroundings.
- They return heat and entropy to their surroundings.
Equilibrium Constant
- For the general reaction aA + bB → cC + dD:
- The equilibrium constant, Keq, is given by: Keq = ([C]^c[D]^d) / ([A]^a[B]^b)
- K > 1: Products are favored at equilibrium
- K < 1: Reactants are favored at equilibrium
- K = 0: The reaction does not proceed to any significant extent
Standard Free-Energy Change
- Standard transformed constants are physical constants based on the biochemical standard state.
- [H+] = 10−7 M
- [H2O] = 55.5 M
- [Mg2+] = 1 mM
- Standard free-energy change: ∆G′°
- Standard equilibrium constant: K′eq
Relationship Between K′eq and ∆G′°
- The relationship between K′eq and ∆G′° is: ∆G′° = -RT ln K′eq
- Standard free-energy change is an alternative mathematical way of expressing the equilibrium constant.
Relationship between Equilibrium Constants and Standard Free-Energy Changes
- If Keq is > 1.0, its ∆G′° is negative.
- If Keq is < 1.0, its ∆G′° is positive.
- The relationship is exponential.
Equilibrium Constant (K'eq) and Free Energy Change (ΔG'°)
- The equilibrium constant (K'eq) describes the extent of a reaction at equilibrium.
- A K'eq greater than 1.0 indicates that the reaction favors product formation at equilibrium.
- A K'eq equal to 1.0 indicates that the reaction is at equilibrium, with no net change in the concentration of reactants or products.
- The standard free energy change (ΔG'°) determines the spontaneity of a reaction.
- A negative ΔG'° indicates a spontaneous reaction, meaning the reaction will proceed forward.
- A ΔG'° of zero indicates that the reaction is at equilibrium.
- Starting with all reactants and products at 1 M concentration, a reaction with K'eq > 1.0 and ΔG'° < 0 will proceed forward.
- This means that the reaction will continue until it reaches a state of equilibrium where the ratio of products to reactants is defined by the equilibrium constant.
Carbonyl Group
- A carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom [C=O]
- The simplest carbonyl groups are aldehydes and ketones.
- Carbonyl groups can be found in many aromatic compounds contributing to smell and taste.
Carbanions
- A carbanion is stabilized by an adjacent carbonyl group.
- Carbanions are nucleophiles.
Bond Cleavage
- Heterolytic cleavage of a C–C bond yields a carbanion and a carbocation
- Homolytic bond cleavage results in each atom keeping one electron of the shared pair.
- Carbon atoms can exist in five oxidation states.
Carbon-Carbon Bond Formation
- A combination of a nucleophilic carbanion and an electrophilic carbocation forms a C–C bond.
- In biochemistry, carbanions and carbocations are unstable and unlikely to participate in reactions.
Carbonyl Group Chemical Properties
- The carbon of a carbonyl group is an electrophilic carbon.
- Carbonyl and imine groups form carbanions on adjoining carbons by delocalizing electrons.
Common Reactions forming and breaking C-C bonds
- Aldol Condensation, Claisen Condensation, and Decarboxylation reactions involve a carbanion intermediate, stabilized by a carbonyl group.
Carbocations in Carbon-Carbon Bond Formation
- Carbocation intermediates are formed via the elimination of an excellent leaving group, such as pyrophosphate.
Internal Rearrangements, Isomerizations, and Eliminations
- Redistribution of electrons leads to changes in structure (isomeric forms) without changing the overall oxidation state of the molecule.
- These reactions include intramolecular oxidation-reduction, change in cis-trans arrangement at a double bond, and transposition of double bonds.
Elimination Reactions
- Loss of water from an alcohol introduces a C=C bond.
- Similar reactions are possible with eliminations in amines.
Free-Radical Reactions
- Homolytic cleavage of covalent bonds to generate free radicals occur in some reaction pathways.
Group Transfer Reactions
- The transfer of acyl, glycosyl, and phosphoryl groups from one nucleophile to another is common.
- Acyl group transfer involves the addition of a nucleophile.
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Description
Explore the fundamental principles of bioenergetics and thermodynamics in this quiz. Learn about energy transformation in living organisms, the laws of thermodynamics, and the concept of enthalpy. Test your understanding of how living systems interact with their surroundings and the energy changes that occur in chemical processes.
